Metal can bodies are frequently formed with a cylindrical side wall projecting from an integral bottom wall, by a drawing and ironing (D&I) process, as is well known. Beverage cans have a nominal diameter of, for example, two and eleven sixteenths inches (a "211" can). The open end is necked and flanged to, for example, a neck diameter of "206" (two and six sixteenths inches) on the standard 211 can or even to a "204" neck (two and four sixteenths). After the can is filled with a beverage, a can end or lid is sealed onto it by double-seaming.
The purpose of necking the can is to allow the use of a smaller diameter end. The neck enables the flange, and therefore the can end, to be of smaller diameter than if there were no neck, which means further metal reduction and thereby cost savings in metal. Necking also minimizes the radial extent of the flange which is formed at the end of the necked portion and thus helps to resist flange cracking. The neck may also provide a convenient way for a carrier to engage a plurality of cans.
There are various ways of necking a beverage can. One known method involves the use of static necking dies wherein the can is conveyed through a number of stations. At each station, a die ring is relatively reciprocated into contact with the open end while the can bottom is non-rotatably held with a base pad assembly. At each successive station, the static necking die is of progressively smaller diameter to progressively neck the can to the desired diameter.
Other necking methods involve rolling or spinning the neck and/or flange, using an external spinning roll cooperating with an internal member within the can body. In these methods, the can body is supported rigidly by an internal mandrel or the like. The internal member may be a spinning roll, pilot, or mandrel supporting the can body. In one such method, the neck and flange are formed simultaneously in a can body supported internally and rigidly by a mandrel or chuck of an expanding/collapsing type, the neck and flange profile being formed by external spinning rolls cooperating with this mandrel.
In another such method, the can body is supported internally by an anvil and endwise by a spinning pilot; the neck and flange are formed by a profiled, external spinning roll which deforms the can body into a groove on the pilot and anvil, and the roll is moved axially of the can body.
The problems associated with the rolling or spin forming of the neck as used in the prior art identified hereinabove concern the weak and relatively unsupported upper side wall metal of the open end of the can body. Such metal is usually very thin (e.g., about 0.004--0.006 inches), highly worked during ironing and highly grain oriented. Merely placing a tool with the desired profile inside the can and applying a similarly shaped roller to the outside of the can while it is spinning does not give the metal adequate or complete support to prevent wrinkling, cracking, buckling, crushing or tearing during the forming operation. This uncontrolled or unsupported application of radial side force on the thin metal side wall of the open end is unacceptable in connection with operations performed at multiple stations wherein the rate of production of the cans during necking may be as high as 1,500-2,000 cans per minute.
A spin flow necking process and apparatus are disclosed in U.S. Pat. No. 4,781,047, issued Nov. 1, 1988 to Bressan et al, which is assigned to Ball Corporation and is exclusively licensed to the assignee of the present application, Reynolds Metals Company. The disclosure of this patent is hereby incorporated by reference herein in its entirety. It concerns a process where an external free roll is moved inward and axially against the outside wall of the open end of a rotating trimmed can to form a conical neck at the open end thereof. A spring loaded holder supports the interior wall of the can and moves axially under the forming force of the free roll. This is a single operation where the can rotates and the free roll rotates so that a smooth conical necked end is produced. In practice the can is then flanged.
The term "spin flow necking" is used in this application to refer to such processes and apparatus, the essential difference between spin flow necking and other types of spin necking being the axial movement of both the external roll and the internal support.
Spin flow necking as described above offers the potential of making a 204, 202, 200, or even smaller neck on a standard 211 can, in a single multiple-station machine. Spin flow necking also offers can wall thickness reductions because of the lower necking load requirements imposed on the can during necking. Spin flow necking also has the potential for minimizing flange width variations, and the resulting can has a smooth profile and an attractive appearance. However, to make spin flow necking truly effective as a viable production process, it is necessary to incorporate a large number of spin flow necking stations in a machine having can handling capabilities permitting a throughput of approximately 1,500-2,000 cans per minute. Such a machine must be capable of rapidly and reliably feeding cylindrical can bodies onto the spin flow necking assemblies at a high production speed and must be capable of supporting the can bottom walls both quickly and in true alignment with the spin flow necking tooling. Such a machine must also preferably have the capability of preventing tool-to-tool contact between the surfaces of the spin flow necking tools during periods of disruption in can supply to prevent early wear and replacement of these extensive tools. To our knowledge, there is no previously known method or machine for providing adequate support or complete positive control over the cans during spin flow necking so that these requirements can be met.
It is accordingly one object of the present invention to provide a combination of an external roller and an internal holder which cooperate to overcome the problems of metal damage during a necking operation by means of spin flow necking.
Another object of the invention is to disclose a holder which co-acts with a forming roller to provide continuous support for the metal being spin flow formed into a neck in a machine having multiple spin flow necking stations for necking metal cans at each station down to a desired necked diameter.
Another object is to provide a spin flow necking machine capable of handling a large number of can bodies successively fed to the machine by ensuring that the can bodies are quickly and reliably retained in the machine in true alignment with the spin flow necking tooling and with sufficient clamping force applied to the can end walls to support the can during necking.
Another object is to ensure that the can bodies are easily and rapidly mounted in centering alignment with the spin flow necking tooling.
Still another object is to ensure that spin flow necking occurs at each station with adequate and complete support to the can to prevent wrinkling, cracking, buckling, crushing or tearing of the can side wall.
Still another object is to prevent uncontrolled or unsupported application of radial side force on the can open end by the spin flow forming roller.
Yet another object is to provide a multi-station spin flow necking machine having lower necking load requirements.
Still another object is to provide a multi-station spin flow necking machine which has high production throughput at manufacturing speeds in excess of 1,500 cans per minute.
Another object is to provide a multi-station spin flow necking machine which is capable of rugged and reliable operation in a hostile can making environment of a 24-hour a day aluminum fines atmosphere.